Looks fine to me. Anything else is just aesthetics (making it look pretty). To that end you might try some masonry patterns on the walls, some shadows, some torches on the walls, stuff like that. Depends on what sort of mood you're trying to set...a temple basement, a dark and creepy basement under a spooky house, a barracks store room. All of that stuff takes time and practice so I'd check out some of the finished maps and see if there are things in those maps that you could incorporate style-wise. The main thing, though, is that this looks good as is, clear and straight-forward without a bunch of junk to clutter it up.